oe.path: Add copyhardlink() helper function

This function creates hard links if possible, falling back to copying
the file if the destination is on a different volume to the source.

The docstring for copyhardlinktree() is also updated to make the
difference between the two functions a little clearer.

(From OE-Core rev: 5437efa16f9bec914e417c6c939a39c247084f52)

Signed-off-by: Paul Barker <paul@betafive.co.uk>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oe/path.py

@@ -90,7 +90,7 @@ def copytree(src, dst):
     subprocess.check_output(cmd, shell=True, stderr=subprocess.STDOUT)
 
 def copyhardlinktree(src, dst):
-    """ Make the hard link when possible, otherwise copy. """
+    """Make a tree of hard links when possible, otherwise copy."""
     bb.utils.mkdirhier(dst)
     if os.path.isdir(src) and not len(os.listdir(src)):
         return
@@ -114,6 +114,17 @@ def copyhardlinktree(src, dst):
     else:
         copytree(src, dst)
 
+def copyhardlink(src, dst):
+    """Make a hard link when possible, otherwise copy."""
+
+    # We need to stat the destination directory as the destination file probably
+    # doesn't exist yet.
+    dstdir = os.path.dirname(dst)
+    if os.stat(src).st_dev == os.stat(dstdir).st_dev:
+        os.link(src, dst)
+    else:
+        shutil.copy(src, dst)
+
 def remove(path, recurse=True):
     """
     Equivalent to rm -f or rm -rf